3D Reconstruction of Bias Effects on Porosity, Alignment and Mesoscale Structure in Electrospun Tubular Polycaprolactone
Authors:
Y. Liu,
F. J. Chaparro,
Z. Gray,
J. Gaumer,
D. B. Cybyk,
L. Ross,
P. Gosser,
Z. Tian,
Y. Jia,
T. Dull,
A. L. Yarin,
J. J. Lannutti
Abstract:
Porosity variations in tubular scaffolds are critical to reproducible, sophisticated applications of electrospun fibers in biomedicine. Established laser micrometry techniques produced ~14,000 datapoints enabling thickness and porosity plots versus both the azimuthal (Phi) and axial (Z) directions following cylindrical mandrel deposition. These 3D datasets could then be "unrolled" into "maps" reve…
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Porosity variations in tubular scaffolds are critical to reproducible, sophisticated applications of electrospun fibers in biomedicine. Established laser micrometry techniques produced ~14,000 datapoints enabling thickness and porosity plots versus both the azimuthal (Phi) and axial (Z) directions following cylindrical mandrel deposition. These 3D datasets could then be "unrolled" into "maps" revealing variations in thickness and porosity versus 0, -5, and -15 kV collector bias. As bias increases, thinner, more "focused" depositions occur. Simultaneous decreases in net porosity versus bias (91.1% 0kV > 83.4% -5kV > 80.2% -15 kV) are sensible, but significant changes in the distribution were unexpected. Surprisingly, at 0 kV, extensive mesoscale surface roughness is evident. Optical profilometry revealed unique features ~1600-420 mum in size, standing ~210 mum above the surrounding surface. These shrink to only ~440-150 mum in size and ~30 mum higher at -5 kV bias and disappear entirely at -15 kV. Scanning electron microscopy (SEM) resolved these into novel, localized "domains" containing tightly aligned fibers oriented parallel to the mandrel axis. Unexpectedly, we also observed substantial orientation along the mandrel axis. By modifying classical bending instability models to incorporate cylindrical electric fields, simulation revealed that horizontal components in the modified electric field alter bending loop shape, causing the observed alignment. This provides a new, easily utilized tool enabling facile, efficient tuning of orientation.
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Submitted 18 August, 2021;
originally announced August 2021.
Gravitational Drainage of Thin Films of Trisiloxane-(Poly)ethoxylate Superspreaders
Authors:
Soumyadip Sett,
Rakesh P. Sahu,
Suman Sinha-Ray,
Alexander Yarin
Abstract:
Gravitational drainage of vertical films supported on a wire frame of superspreader SILWET L-77 and its cousin non-superspreader SILWET L-7607 revealed drastic differences. The superspreader films showed complicated dynamic turbulent-like interferometric patterns in distinction from the ordered color bands of the cousin non-superspreader which reminded those of the ordinary surfactants. Neverthele…
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Gravitational drainage of vertical films supported on a wire frame of superspreader SILWET L-77 and its cousin non-superspreader SILWET L-7607 revealed drastic differences. The superspreader films showed complicated dynamic turbulent-like interferometric patterns in distinction from the ordered color bands of the cousin non-superspreader which reminded those of the ordinary surfactants. Nevertheless the superspreader films stabilized themselves at the thickness below 50 nm and revealed an order of magnitude longer life time before bursting compared to the cousin non-superspreader. Notably, the superspreader revealed drastic differences from the non-superspreader in aqueous solutions with no contact with any solid Teflon surface. The theoretical part of the work attributed the self-stabilization of the superspreader films to significant disjoining pressure associated with the van der Waals repulsion of the fluffy surfaces of the film formed by long superspreader bilayers hanging from the free surfaces. The non-superspreaders do not possess any significant disjoining pressure in the film with thicknesses even in the range 30-50 nm. The results show that gravitational drainage of vertical films is a useful simple tool for measuring disjoining pressure.
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Submitted 17 July, 2013;
originally announced July 2013.